Heating unit



Patented May 1, 1928.

UNITED STATES PATENT oFFicE.

CLYDE C. HARPSTER AND WILLIAMi B. KING, 0F MANSFIELD, OHIO, ASSIGNORS T0 WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A. CORPORATION 0I' PENNSYLVANIA.

Application led Apri12,

Our invention relates to electric heaters and particularly to encased tubular heating units.

An object ot our invention is to provide a relatively simple and highly eflicient encased tubular heating unit that may be bent to any desired shape.

In practicing our invention, we provide a tubular metal casing, an open helix of resistor Wire in the casing, masses of expansively-oxidized electric-insulating material within and without said helix and a closing bushing at each end of the casing.

In the single sheet of drawings,

Figure 1 is a View, partially in side elevation and partially in longitudinal section, of

f an unfinished electric heater embodying our invention.

Fig. 2 is a fragmentary view, in longitudinal section, of an end portion of an uniinished heater, on an enlarged scale.

Fig. 3 is a view of an end portion, in lon.- gitudinal section, of a. treated heating unit embodying 'our invention, on an enlarged scale, and.

Fig. 4 is a'view. in lateral section therethrough, taken on the line IV-IV of Fig. 3.

An electric heater, designated by the numeral 11, comprises an outer tubular metal casing 12 that may be of any suitable metal which will withstand the temperature at which it is to be operated. Thus, for relatively low-temperature heaters, copper tubes may be used, and, for higher temperatures, steel or special-alloy-steel tubes may be used. The tubular casing 12 should be of such dimensions, as to thickness of the wall thereof, that it can be bent into any desired shape, one form being shown in Fig. 1 as of substantially U-shape.

An open helix 13 of a suitable resistor wire, such as nichrome, is wound on a mandrel and then removed therefrom. An open helix 14 is made of a strip of metallic 'magnesium wound flatwise (see Fig. 2) and is located around the open helix 13 of resistor wire. A bundle 15 of rods, bars, Wires or strips of metallic magnesium is located within thev helix 13, a sufficient number of individual bars or strips being employed to tit relatively closely within the helix. After providing a reinforced terminal lead 16 connected tothe resistor at each end thereof, which reinforcement may be made by douthe casing 12.

HEATING UNIT.

1927. Serial N0. 180,891.

bling over the end portion of the resistor and twisting it as shown more particularly in Figs. 2 and 3 of the drawing, the resistor helix and the magnesium elements within and without the helix are located in the tubular casing 12, substantially as shown in Fig. 2. We prefer to make the longitudinal extent of the helix 13 somewhat less than the overall length of the casing 12 and to make the reinforced terminals 16 extend for an appreciable distance into the end portions of lThe heating unit thus assembled is then located within an autoclave or a suitable closed casing, and subjected, for a length of time, to the action o high-temperature steam, in a manner more particularly disclosed and claimed in reissued Patent No. 16,340 to C. B. Backer. The treatment thus given will aect the condition of the initially metallic magnesium members 14 and 15, and expansively oxidize them into magnepredetermined sium hydroxide or oxide. During this` change, the initially metallic magnesium expands to substantially 200% of its initial volume, so that the open helix 14 located outside ofthe resistor helix 13 will tightly compress the resistor within the tubular casing 12. The action of the steam u on the helix 14 ot metallic magnesium, in c anging it to hydroxide or oxide, is such as to change it to a substantially solid crystalline tubular mass within the casing 12 and outside the helix 13, although portions of the mass oi oxide will extend between the spaced .turns of the resistor wire. The inner magnesium member 15 will, of course, also ex and and will grow outwardly, so that it wi l tend to open up the individual turns of the resistor wire 13 and force them outwardly against. the outer tubular crystalline mass of magnesium hydroxide or oxide.

The mass of magnesium hydroxide or oxidc thus formed is, in eiect, a relatively large crystal rather than a mass composed of a large number of individual smaller crystals. This has the result of providing a highly eicient heat path from the resistor wire to the inner surface of the tubular casing 12, so that there will be only a relatively small temperature di'erential between the resistor wire and the tubular casing itself.A

The amount of initiall metallic magnesium provided Within t e casing 12 and closely adjacent te the ends thereof is such that 1t will tightly grip the reinforced terminal lead 16 to hold it securely in its proper operative position within the casing.

The outer ends of the casing 12 may be provided with an enlarged bore 17 in order to provide a shoulder against which the inner surface of a bushing 18 of electricinsulating material may fit. The bushing 18 has two different external diameters, and that portion havin the larger diameter fits into the enlarged ore 17, substantially as shown in Figs. 2 and 3 of the drawing. rlhe outer or extreme end portion of the casing 12is spun over against the reduced portion of the bushing 18, as shown more particularly in Fig. 3 of the drawing, by which means the bushing 18 is rmly held in its proper operative position.

The use of the inner member 15 of ini- `tially metallic magnesium and nally expansively-oxidized magnesium hydroxide or oxide is important when it is desired to bend the tubular casing 12 to any form, a simple form being shown in Fig. 1, as noted above. If the inner mass of expansively-oxidized magnesium hydroxide or oxide were not provided, there would be danger of accidental contact between the spaced turns of resistor wire, at the point where the casing is bent on a small'radiu's. This danger is entirely overcome in a device ofthe kind described hereinbefore.

While we have illustrated and described a device and a method embodying our invention, as applied more particularly to a tubular heating element, it is not necessarily limited thereto, as we may locate the helix of resistor wire, together with the outer and the inner initially metallic magnesium members, in a suitable groove in a metal member which is to be heated and treat the same in situ in the manner described above in connection with these members whenV located in the casing 12.

Various modications may be made in the neer/,ear

'forth in the appended claims.

lWe claim as our invention:

1. The method of manufacturing an encased tubular heating unit which comprises locating an open helix of resistor'wire within an opcn helix of magnesium metal, locating a plurality of rods of magnesium metal Within said helix and coextensive therewith, locating said resistor and magnesium members within a tubular metal casing and subjecting the assembly to the action of highpressure 'steam to expansively oxidize the magnesium members into crystalline masses of electric-insulating magnesium oxide.

2. rlhe method of making tubular encased heaters, which comprises locating metallic magnesium members outside and inside of an open helix of resistor Wire, locating said resistor and magnesium members within a metal tube, and subjecting the assembly to the action of steam at high temperature to expansively oxidize the magnesium members to tightly hold the resistor in the metal tube and to provide a high-conductivity heat lpath from the resistor to the metal tube.

3. A method of making a tubular heater having a heating 'coil that comprises placing initially metallic expansively oxidizable material within the coil and oxidizing said material. c

4. The method of making a tubular heater having a heating coil that comprises placing initially metallic expansively oxidizable material both within and Without the coil and oxidizing said material.

ln testimony whereof, we have hereunto subscribed our names this 21st day of March, 1927. 

